An unusual parable about our perception of life

A professor, speaking to an audience, told a joke. It was one of those funny anecdotes from life that can cheer everyone up..... And when he finished, the whole audience gasped with laughter.

After about 15 minutes, the lecturer told the same joke again. This time only a few people smiled, while most looked at each other in surprise, shrugging their shoulders. Some even frowned, probably wondering whether the lecturer had a good memory.

Half an hour later, the professor told the same joke a third time, but no one else laughed.

The lecturer looked around at the audience and said: "You can't laugh at the same joke all the time... So why do you allow yourself to cry at the same thing all the time?"